hive查询hbase

背景

hbase查询的确是不太方便，除了指定rowkey，或者通过指定startkey stopkey进行scan之外，没有更有效的查询方式 如果想通过列值过滤，只能全表扫描了 如果要搞什么group by或者order by（除非你的rowkey做了相应设计） 更是没法弄 在传统的mysql/oracle得心应手的查询在hbase上就是束手束脚

当然可以通过写hadoop job解决问题，但为了查询去写job，代价未免有点高 于是hive出现了

有两个方法可以集成hive和hbase

1. 使用HBaseStorageHandler，这个会直接操作HBase,可能会对线上产生影响
2. 将HBase定期导入到HDFS，再通过hive访问HDFS

下面将详述第二种方法

HDFS导入

1. 使用datax将HBase表导入到HDFS上,比如/group/wireless-arctic/task/arctic_task

2. hive产生外部表，从而避免导入数据

    CREATE EXTERNAL TABLE task_history ( biz_type string, cid string, content string, ctime string, gmt_create string, hostName string, item string, mtime string, otags string, priority string, retry string, result string, srcImages string, src_url string, status string, summary string, task_type string, title string, userId string, userNick string, utags string, writer string ) ROW FORMAT DELIMITED FIELDS TERMINATED BY '\001' LOCATION '/group/wireless-arctic/task';

   location是云梯文件的目录

3. 测试

    select cid,result from task_history limit 10; Total MapReduce jobs = 1 Launching Job 1 out of 1 Number of reduce tasks is set to 0 since there's no reduce operator Selecting distributed mode: Input Size (= 2578823293 = 2 gigabytes 411 megabytes 366 kilobytes 125 bytes) is larger than hive.exec.mode.local.auto.inputbytes.max (= 134217728 = 128 megabytes 0 kilobytes 0 bytes) Starting Job = job_201311281255_6734353, Tracking URL = http://hdpjt2.alibaba-inc.com/jobdetails.jsp?jobid=job_201311281255_6734353 Kill Command = /home/hadoop/hadoop-current/bin/../bin/hadoop job -Dmapred.job.tracker=hdpjt:9001 -kill job_201311281255_6734353 Hadoop job information for Stage-1: number of mappers: 10; number of reducers: 0 2013-12-19 18:53:02,891 Stage-1 map = 0%, reduce = 0% 2013-12-19 18:53:11,017 Stage-1 map = 50%, reduce = 0% 2013-12-19 18:53:12,033 Stage-1 map = 90%, reduce = 0% 2013-12-19 18:53:19,394 Stage-1 map = 100%, reduce = 100% Ended Job = job_201311281255_6734353 OK 200011928538 success 200011928538 success 200011909281 success 200011928474 success 200011909281 success 200011928474 success 110010569498 failure:userId:1782836127,contentId:110010569498 ImageFlow,call error and ret:1 110010523403 success 110010523921 success 110010524299 success Time taken: 23.137 seconds = 23 seconds 137 milliseconds

添加分区及自动化

1. 完成了上面的步骤，你就可以查询数据了，但面临一个问题，数据更新怎么办？

   • 一个比较通用的做法就是每天跑一个定时任务将HBase表dump到HDFS，即每天一个快照
   • 每天的快照可以存放在以日期命名的目录中，这样可以保存多份快照，出了问题也好追踪

2. hive如何利用这每天的快照?

   • 那就是hive分区
   • 分区的本意是数据量大了切分数据,但目前我们并未如此使用，而是利用分区来区分快照
   • 删除之前的表

     drop table task_history;

   • 产生一张分区表

     CREATE EXTERNAL TABLE task_history ( biz_type string, cid string, content string, ctime string, gmt_create string, hostName string, item string, mtime string, otags string, priority string, retry string, result string, srcImages string, src_url string, status string, summary string, task_type string, title string, userId string, userNick string, utags string, writer string ) PARTITIONED BY (dt string) ROW FORMAT DELIMITED FIELDS TERMINATED BY '\001' LOCATION '/group/wireless-arctic/task';

     其实就是在之前的建表语句中加了一行PARTITIONED BY (dt string)
   • 添加分区

     ALTER TABLE task_history ADD PARTITION(dt='20131223') LOCATION '/group/wireless-arctic/task/20131223';

3. 如何自动化

   • 通过工具比如datax或者其他导出工具将HBase表导出到HDFS,正如前面提到的每天一个目录（以日期命名）
   • 将每天的数据目录挂载到hive分区

     hive -e "ALTER TABLE task_history ADD PARTITION(dt=`date -d yesterday +%Y%m%d`) LOCATION '/group/wireless-arctic/task/`date -d yesterday +%Y%m%d`';"

   • 将前面2个步骤的脚本整合到crontab 中就可以做到自动化了
   • 最后如何通过分区查询

     select * from task_history where dt='20131223' limit 10;

     即加上分区查询条件dt='20131223'